1. Field of the Invention
The present invention relates to a toner for developing an electrostatic charged image in an image forming method such as the electrophotography method or the electrostatic recording method.
2. Related Background Art
As electrophotography methods, various methods have conventionally been proposed in, for example, the U.S. Pat. No. 2,297,691, Japanese Patent Publication No. 42-23910 and Japanese Patent Publication No. 43-24748.
The electrophotography methods are broadly classified into the dry development method and the wet development method. The former further divided into a method using a two-component developing agent and a method using a one-component developing agent.
As a toner applied in these dry development methods, a fine powder prepared by dispersing a dyestuff or a pigment in a binder resin is used. For example, particles prepared by finely dividing a mixture formed by dispersing a coloring agent in a binder resin such as polystyrene to a size of from about 1 to 30 .mu.m are used as toner particles. A toner containing magnetic particles such as magnetite is employed as a magnetic toner. In the case of a two-component developing agent, a toner is usually used in mixture with such carrier particles as iron powder or magnetic ferrite particles.
Along with the recent tendency toward more personal uses, a higher speed, and more diversified functions, there is an increasing demand for a toner which is excellent in environmental stability and durability, gives a high image density, is free from fogging, is rich in resolution, and is capable of forming an image clear in contrast and excellent in gradation. More recently, furthermore, such new manners of development as reversal development, digital development and low-potential development are being used in addition to positive development and analog development, and a toner capable of forming a high-quality toner image in any of these development practices is demanded.
In order for a toner to satisfactorily cope with any of these development methods, it is important that triboelectric characteristics of the toner is sufficiently controlled.
When causing a toner to retain a charge, while it is possible to utilize triboelectric characteristics of a binder resin, a binder resin has generally only a low triboelectric property. An image formed with such a toner is susceptible to fogging and is not clear. For this reason, it is the common practice to add a dyestuff or a pigment for controlling triboelectric property, or even a charge controlling agent to impart a desired triboelectric property to a toner.
Charge controlling agents known at present in the referred technical area include, as positive triboelectric materials, Nigrosine dyestuff, azine based dyestuff, copper phthalocyanine based pigment, quarternary ammonium salt, and polymers having quarternary ammonium salt in a side chain, and as negative triboelectric materials, metal complexes of monoazo dyestuff, metal complex salts of salicylic acid, alkylsalicylic acid, dialkylsalicylic acid, naphthoic acid, dicarboxlic acid, and resins having acid groups. These charge controlling agents are proposed in Japanese Patent Publication No. 41-20153, Japanese Patent Publication No. 43-17955, Japanese Patent Publication No. 45-26478, and Japanese Patent Publication No. 55-42452.
A toner containing a compound having an Al salt structure is proposed in Japanese Patent Application Laid-Open No. 63-237065 and Japanese Patent Application Laid-Open No. 5-197207 (the corresponding U.S. Pat. No. 5,324,613). For this toner, triboelectric property differs between low and high values of humidity, and the toner is thus largely affected by environmental conditions. A toner containing a compound having an Al complex structure is proposed in Japanese Patent Application Laid-Open No. 63-208865 (the corresponding U.S. Pat. No. 4,845,003). In this toner, the development property after continuous copying in a low humidity is different from the initial one, thus resulting in large fluctuations caused by continuous use for multiple runs of copying.
There is therefore a demand for a toner, particularly a color toner, excellent in environmental stability and multiple-copy durability.